There are known many antibiotics which are produced by microorganisms of the genus Streptomyces and which are useful as antibacterial agent and/or as an antitumor agent for the inhibition of experimental animal tumors. In an attempt to obtain further new antibiotics, we collect various soil samples, isolate microorganisms from soil samples and investigate metabolic products as produced by aerobic cultivation of the isolated microorganisms. We isolated a new microorganism from a soil sample collected at Nishi-shinagawa, Shinagawa-ku, Tokyo, Japan, and we have designated this new isolated microorganisms as MF266-g4 strain. This strain has been confirmed to belong to the genus Streptomyces. We have succeeded to cultivate the MF266-g4 strain, produce and accumulate a new substance designated as MF266 substance in the culture of said strain and isolate the new substance from the culture.
We have now found that the isolated new substance, MF266 substance strongly inhibits the growth of various gram-positive bacteria and also inhibits effectively the growth of mouse leukemia L-1210 cell and is a new antibiotic.